Northern Hemisphere

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Coordinates: 45°0′0″N 0°0′0″E / 45°N 0°E / 45; 0

The Northern Hemisphere[1] is the half of a planet that is north of equator—the word hemisphere literally means 'half sphere'. It is also that half of the celestial sphere north of the celestial equator. Earth's northern hemisphere contains most of its land area and most of its human population (about 90%).

See also Arctic, Temperate zone, Tropics, Seasons and Climate

Due to the Earth's axial tilt, winter lasts from the winter solstice (typically December 22) to the vernal equinox (typically March 20), while summer lasts from the summer solstice (typically June 21) through to the autumnal equinox (typically September 21).

The Arctic is the region north of the Arctic Circle. Its climate is characterized by cold winters and cool summers. Precipitation mostly comes in the form of snow. The Arctic experiences some days in summer on which the sun never sets, and some days in winter on which the sun never rises. The duration of these phases varies from one day for places right on the Arctic Circle to several months near the North Pole itself.

Between the Arctic Circle and the Tropic of Cancer lies the Northern Temperate Zone. The changes in these regions between summer and winter are generally mild, rather than extreme hot or cold. However, a temperate climate can have very unpredictable weather.

Tropical regions (between the Tropic of Cancer and the equator) are generally hot all year round and tend to experience a rainy season during the 'summer' months, and a dry season during the 'winter' months.

In the northern hemisphere, objects moving across or above the surface of the Earth tend to turn to the right because of the Coriolis effect. As a result, large-scale horizontal flows of air or water tend to form clockwise-turning gyres north of the equator. These are best seen in ocean circulation patterns in the North Atlantic and North Pacific Oceans. South of the equator, the directions are reversed.

For the same reason, flows of air down toward the northern surface of the Earth tend to spread across the surface in a clockwise pattern. Thus, clockwise air circulation is characteristic of high pressure weather cells in the northern hemisphere. Conversely, air rising from the northern surface of the Earth (creating a region of low pressure) tends to draw air toward it in a counterclockwise pattern. Hurricanes and tropical storms (massive low-pressure systems) spin anti-clockwise in the northern hemisphere (by contrast, they spin clockwise in the southern hemisphere).

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